The effect of age and diet on the cellular protein synthesis of liver of male mice

The rates of cellular protein synthesis were estimated in liver by determining: 1) the half lives of proteins by the rate of disappearance of radioactivity following the intraperitoneal injection of C14 labeled sodium bicarbonate, and 2) the cellular protein levels estimated by the concentration of proteins and DNA of the tissue. The age studies were carded out on C57BL/6J mice, aged 12, 18, 24, and 32–34 months, fed the NIH Open Formula Mouse Diet. Dietary studies were carried out on 9 month old B6D2F1 mice fed purified diets which contained crude casein. The animals were offered one of the following regimens. One group was fed a 24% protein diet ad libitum. Another group was fed a 4% protein diet ad libitum. The third and fourth groups were fed the 24% protein diet ad libitum for twenty-four hours on Monday and Wednesday, and for eight hours on Friday. The third group was sacrificed following a 24 hour feeding period, while the fourth group wee sacrificed following a 24 hour fasting period. The rates of disappearance of radioactivity from the liver proteins of mice were not statistically significantly affected by age or dietary regimens. However, there was a 27% progressive decrease in the cellular protein synthesis of liver between the ages of 12 and 32–34 months. Feeding a low protein diet ad libitum resulted in a 28% decrement. In addition, during the 24 hour period of starvation during intermittent feeding, there is a 30% decrease in cellular protein synthesis which returns to normal levels during the 24 hour feeding period.